1. Field of the Invention
This invention relates to novel compounds which are potent and highly selective inhibitors of isolated factor Xa or when assembled in the prothrombinase complex. These compounds show selectivity for factor Xa versus other proteases of the coagulation (e.g. thrombin, fVIIa, fIXa) or the fibrinolytic cascades (e.g. plasminogen activators, plasmin). In another aspect, the present invention relates to novel monoamidino-containing compounds, their pharmaceutically acceptable salts, and pharmaceutically acceptable compositions thereof which are useful as potent and specific inhibitors of blood coagulation in mammals. In yet another aspect, the invention relates to methods for using these inhibitors as therapeutic agents for disease states in mammals characterized by coagulation disorders.
2. Background of the Invention
Hemostasis, the control of bleeding, occurs by surgical means, or by the physiological properties of vasoconstriction and coagulation. This invention is particularly concerned with blood coagulation and ways in which it assists in maintaining the integrity of mammalian circulation after injury, inflammation, disease, congenital defect, dysfunction or other disruption. Although platelets and blood coagulation are both involved in thrombus formation, certain components of the coagulation cascade are primarily responsible for the amplification or acceleration of the processes involved in platelet aggregation and fibrin deposition.
Thrombin is a key enzyme in the coagulation cascade as well as in hemostasis. Thrombin plays a central role in thrombosis through its ability to catalyze the conversion of fibrinogen into fibrin and through its potent platelet activation activity. Direct or indirect inhibition of thrombin activity has been the focus of a variety of recent anticoagulant strategies as reviewed by Claeson, G., “Synthetic Peptides and Peptidomimetics as Substrates and Inhibitors of Thrombin and Other Proteases in the Blood Coagulation System”, Blood Coag. Fibrinol. 5:411–436 (1994). Several classes of anticoagulants currently used in the clinic directly or indirectly affect thrombin (i.e. heparins, low-molecular weight heparins, heparin-like compounds and coumarins).
A prothrombinase complex, including Factor Xa (a serine protease, the activated form of its Factor X precursor and a member of the calcium ion binding, gamma carboxyglutamyl (Gla)-containing, vitamin K dependent, blood coagulation glycoprotein family), converts the zymogen prothrombin into the active procoagulant thrombin. Unlike thrombin, which acts on a variety of protein substrates as well as at a specific receptor, factor Xa appears to have a single physiologic substrate, namely prothrombin. Since one molecule of factor Xa may be able to generate up to 138 molecules of thrombin (Elodi et al., Thromb. Res. 15:617–619 (1979)), direct inhibition of factor Xa as a way of indirectly inhibiting the formation of thrombin may be an efficient anticoagulant strategy. Therefore, it has been suggested that compounds which selectively inhibit factor Xa may be useful as in vitro diagnostic agents, or for therapeutic administration in certain thrombotic disorders, see e.g., WO 94/13693.
Polypeptides derived from hematophagous organisms have been reported which are highly potent and specific inhibitors of factor Xa. U.S. Pat. No. 4,588,587 describes anticoagulant activity in the saliva of the Mexican leech, Haementeria officinalis. A principal component of this saliva was shown to be the polypeptide factor Xa inhibitor, antistasin (ATS), by Nutt, E. et al., “The Amino Acid Sequence of Antistasin, a Potent Inhibitor of Factor Xa Reveals a Repeated Internal Structure”, J. Biol. Chem., 263:10162–10167 (1988). Another potent and highly specific inhibitor of Factor Xa, called tick anticoagulant peptide (TAP), has been isolated from the whole body extract of the soft tick Ornithidoros moubata, as reported by Waxman, L., et al., “Tick Anticoagulant Peptide (TAP) is a Novel Inhibitor of Blood Coagulation Factor Xa” Science, 248:593–596 (1990).
Factor Xa inhibitory compounds which are not large polypeptide-type inhibitors have also been reported including: Tidwell, R. R. et al., “Strategies for Anticoagulation With Synthetic Protease Inhibitors. Xa Inhibitors Versus Thrombin Inhibitors”, Thromb. Res., 19:339–349 (1980); Turner, A. D. et al., “p-Amidino Esters as Irreversible Inhibitors of Factor IXa and Xa and Thrombin”, Biochemistry, 25:4929–4935 (1986); Hitomi, Y. et al., “Inhibitory Effect of New Synthetic Protease Inhibitor (FUT-175) on the Coagulation System”, Haemostasis, 15:164–168 (1985); Sturzebecher, J. et al., “Synthetic Inhibitors of Bovine Factor Xa and Thrombin. Comparison of Their Anticoagulant Efficiency”, Thromb. Res., 54:245–252 (1989); Kam, C. M. et al., “Mechanism Based Isocoumarin Inhibitors for Trypsin and Blood Coagulation Serine Proteases: New Anticoagulants”, Biochemistry, 27:2547–2557 (1988); Hauptmann, J. et al., “Comparison of the Anticoagulant and Antithrombotic Effects of Synthetic Thrombin and Factor Xa Inhibitors”, Thromb. Haemost., 63:220–223 (1990); and the like.
Others have reported Factor Xa inhibitors which are small molecule organic compounds, such as nitrogen containing heterocyclic compounds which have amidino substituent groups, wherein two functional groups of the compounds can bind to Factor Xa at two of its active sites. For example, WO 98/28269 describes pyrazole compounds having a terminal C(═NH)—NH2 group; WO 97/21437 describes benzimidazole compounds substituted by a basic radical which are connected to a naphthyl group via a straight or branched chain alkylene, —C(═O) or —S(═O)2 bridging group; WO 99/10316 describes compounds having a 4-phenyl-N-alkylamidino-piperidine and 4-phenoxy-N-alkylamidino-piperidine group connected to a 3-amidinophenyl group via a carboxamidealkyleneamino bridge; and EP 798295 describes compounds having a 4-phenoxy-N-alkylamidino-piperidine group connected to an amidinonaphthyl group via a substituted or unsubstituted sulfonamide or carboxamide bridging group.
Still further, drug-induced QT prolongation on hearts has been recently recognized to cause adverse and fatal side-effects in many clinical settings (Netzer, R., et al. Drug Discovery Today, 6:78 (2001)). Several drugs were withdrawn from the market due to their hERG binding and attending QT interval prolongation, for example, Terfenadine (Seldane®, Cisapride (Propulsid®), and astemizole (Hismanal®)). See Pearlstein, R. A., et al., Bioorg. Med. Chem. Lett. 13:1829 (2003).
The hERG potassium channel is human ether-a-go-go-related gene that is expressed in the human heart, and is a key effector of cardiac repolarization, and contributes to the QT interval measured by ECG. It has been shown that inhibition of hERG potassium channel can lead to a prolongation of the QT interval, widely considered a critical risk factor for torsades de pointes (TdP) arrhythmia. Thus, hERG binding has been becoming a major hurdle in current drug development. Fortunately, the high throughput preclinical in vitro assays that measure compound's ability to inhibit hERG channel have become powerful screening tools for medicinal chemists to gain first hand SAR information and to evaluate their potential side-effect in early stage of drug discovery. See Haverkamp, W.; et al. Cardiovasc. Res. 47:219 (2000). Finlayson, K.; et al., European Journal of Pharmacology 430:147 (2001).
Significant progress has been made during the last few years, in the understanding of electrophysiology of hERG channels, mechanisms of drug-induced QT prolongation, the structural understanding of drugs binding to hERG channel, the relationship of hERG binding potency with preclinical in vivo QT prolongation studies (Redfern, W. S., et al., Cardiovasc. Res. 58:32 (2003)). Thus, it is highly desirable to find new compounds that provide beneficial anti-thrombotic activity with little or no hERG binding.
There exists a need for effective therapeutic agents for the regulation of hemostasis, and for the prevention and treatment of thrombus formation and other pathological processes in the vasculature induced by thrombin such as restenosis and inflammation. In particular, there continues to be a need for compounds which selectively inhibit factor Xa or its precursors. Compounds that have different combinations of bridging groups and functional groups than compounds previously discovered are needed, particularly compounds which selectively or preferentially bind to Factor Xa. Compounds with a higher degree of binding to Factor Xa than to thrombin are desired, especially those compounds having good bioavailability and/or solubility.